Counting Fish: on the artificial reefs

We see fish. Big schools of them, swimming around artificial reefs in the Gulf of Mexico, not far from the Texas shore.

Image from a cut-off artificial reef site (MI-712). This gives you an idea of the sheer volume of fish on these structures 95 feet deep. Image pulled from the Go Pro video.

These reefs have been created from parts of oil and gas platforms, Liberty ships, and concrete and other materials to provide habitat for marine life. Many scientists believe such structures actually increase the productivity of a marine ecosystem, meaning there are more fish in the sea than there would be without them, but there isn’t much science to prove this. As I reported in the previous post, a two year study underway at the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University Corpus Christi seeks to quantify how various types of artificial structures affect species abundance and variety.

Texas has 66 artificial reef sites, and HRI plans to survey 15 of them multiple times this year and next. As of a few weeks ago, the research team had visited six of the sites (cutoffs).

Image from the Go Pro video.

If it seems the survey work is off to a slow start, keep in mind that it depends on boat availability and weather. The scientists need seas less than three feet, and gentle currents. A 13-pound ROV gets knocked around in anything over two knots, and for divers, just getting to cut-off or toppled rigs 85 to 90 feet below the surface can be a challenge in a strong current. (I’ve been diving in the Gulf when strong currents had divers flapping on the safety stop line like flags in a stiff wind.)

Calm seas and light currents have to coincide with boat availability, which can be a problem in general. In fact, access has become a huge issue with ocean-related research in general - ships are expensive to maintain and to use, and the number of them available to scientists has declined drastically in recent years.

Scalloped hammerhead taken from the Go Pro video mounted on top of the ROV, also at MI-712.

Texas A&M’s 180-foot vessel, the Gyre, retired in 2005, and The University of Texas took the 105-foot Longhorn out of service in 2007. Twenty-one oceanographic research vessels (big enough to work out in the open sea) are currently available for rent from the University-National Oceanographic Laboratory System (UNOLS) Council, which includes some 61 academic institutions. That’s not even one ship for every two institutions, though, and a single vessel is based in the Gulf of Mexico. Some of those 21 are set to be mothballed in the next few years, too. No surprise, demand for vessels regularly exceeds availability. (I wrote about this issue shortly after Deepwater Horizon, for Nature)

So far, the HRI team has been using the Mo Azul, a 43- foot charter fishing boat based in Port Aransas, for ROV based surveys. It can easily accommodate HRI’s VideoRay Pro4 ROV. The dive-based survey trips go aboard Out to Sea Adventures’ 38-foot Pearson, the Orion. See a photo of it here. The boat is adequate for this project, which takes place mostly within a few hours of shore, but the Orion spends a lot of the summer booked for fishing. HRI expects delivery of a brand-new, 36-foot boat some time this fall, which will allow the team to zip out for surveys whenever the weather cooperates.

Greater Amberjack taken from the standard video on the ROVat artificial reef MI-A-7. This gives you an idea of what we see when piloting the ROV and the information that’s always on the screen (date, time, file name, compass heading, depth and temperature). You can see how the video quality is quite different.

Come October, the team will also participate in a research cruise on the Falkor, a 272-foot, newly refitted research vessel of the privately funded Schmidt Ocean Institute. A German fisheries protection vessel in its previous life, the Falkor was refitted for scientific purposes, and recently had its first shakedown cruise from England to Woods Hole, Massachusetts. Its fall Gulf of Mexico cruise is essentially a field trial, and on it, HRI scientists will have access to a working-class ROV to collect data, including multi-beam surveys. These use multiple beams of sound sent from the ship’s hull to create large maps of the seafloor while the ship is underway.

Meanwhile, we plan to putter out on the Orion later this month to dive some stand-up platforms in blue water, assuming the weather cooperates and no fishing tournaments compete for boat time. We expect to continue to see large schools of recreationally and commercially important fish, as well as those colorful kind that are just fun to look at. I promise to provide pictures.

The views expressed are those of the author(s) and are not necessarily those of Scientific American.

ABOUT THE AUTHOR(S)

Melissa Gaskill

A science and environment writer based in Austin, Texas, Melissa Gaskill has a B.S. in zoology from Texas A&M University and a master's in journalism from the University of Texas. She also has a passion for the ocean and writes about it whenever possible for publications such as Nature News, Men's Journal, The New York Times, and many others.

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